Please Help me with some exercises

[IngBaby]

I've started the exercise but there is something wrong. What I am supposed to do is to
ex1:
Calculate the estimated production of: the squares of single digit natural numbers between 3 and n, if it's known the value of the variable n. The result is not as it should be. Where is the problem ?

  #include "stdafx.h"
#include <iostream>
using namespace std;
int main()



{int n,i,P=1;
cout<<"Please give n";
cout<<"n= ";
	cin>>n;
for(i=3;i<=n;i=i+2)
	P=P*i*i;
cout<<P;
cin.get();cin.get();

	return 0;

ex 2
g=∑(j=1(j≠3,4,5))^n+{1/2j+3} in power j/3
ex3
z={x/2 + 3∏(2i+1) where i=1 and goes till n, for 2x>m
x/3-2∑(k+x) where k=1 k≠3,4 for 2x≤m

[Vidminas]

Your code is very hard to read. In the example you posted, you lack a bracket }after return 0; to end main.
Just a tip:
i = i + 2; can be written as i += 2;

writing

cin.get();
cin.get();

twice in a row isn't good.
use

std::cin.clear();
std::cin.ignore(10000, '\n');

Your example, spaced out:

#include "stdafx.h"
#include <iostream>

int main()
{
    using std::cout; using std::cin; using std::endl;

    int n, i, P = 1;

    cout << "Please give n:" << endl;
    cout << "n = ";
    cin >> n;

    for ( i = 3; i <= n; i += 2 )
    {
        P = P * i * i;
    }

    cout << P;

    cin.clear();
    cin.ignore(10000, '\n');

    return 0;
}

As far as I understand you want your program to work like this:

Please give n:
n = 5
9, 16, 25

Am I right?

Try to think about what happens as the program runs, while looking at the code.
P is 1 from the beginning, then the program asks the user what is n.
If the user enters 5, n becomes 5.

Then the for ( i = 3; i <= n; i += 2 ) loop executes.
Replacing the letters by numbers
P = P * i * i; becomes P = 1 * 3 * 3; so P is 9.

Then the condition for ( i = 3; i <= n; i += 2 ) is checked again but this time i is 5. Since i is equal to n the loop executes once more.

This time P = P * i * i; becomes P = 9 * 5 * 5;
so P is 225.

Then the condition for ( i = 3; i <= n; i += 2 ) is checked again.
This time i is 7, so the loop doesn't execute as it's not less than or equal to n.

Then P (225) is output on the screen.

[Bourgond Aries]

@Vidminas

Isn't the use of #include "stdafx.h" necessary in microsoft's visual studio? I'm not sure it was absolutely necessary, but if I recall correctly, I had to include stdafx.h in order to get MSVC to compile at all...

[Vidminas]

@Bourgond Aries

It wasn't so for me, but I updated the example anyway and I added a step-by-step walkthrough of what happens when the program executes.